LU80726A1 - PROCESS FOR PRODUCING SOLID BODIES OF COPPER-ZINC-ALUMINUM ALLOYS - Google Patents

Description

'- 2 - t

The present invention relates to the manufacture of solid bodies of copper-zinc-aluminum alloys, as well as the bodies thus obtained in the form of finished and semi-finished products · "It is known that, under the crystalline modification ß, many alloys Binary and ternary, of copper have particular characteristics such as a pseudo-elasticity, an elastic recovery effect and a reversible elastic recovery effect.

The expression "pseudo-elasticity" means that, when subjected to a mechanical load at temperatures higher than the so-called "Af" temperature, a solid body of the alloy exhibits an elastic elongation clearly greater than that of other metals and, in any case, higher than that obtained at temperatures below the temperature Af. This pseudo-elastic elongation disappears when the load is removed.

The expression "elastic recovery effect" means that after mechanical deformation at a temperature below the so-called "Ms" temperature, a solid body of the alloy spontaneously resumes its initial shape by means of simple heating above the temperature Af mentioned above.

A reversible elastic recovery effect v is observed when the elastic recovery effect has been used successively several times (for example, 20 times). Then, during cooling down to a temperature below the Ms temperature, a solid body of the alloy undergoes spontaneous deformation without any external mechanical load. This deformation can be suppressed by heating above the aforementioned temperature Af.

The above phenomena are attributable to martensitic transformations, that is to say a rever-

The temperature Ms is the temperature at which these; First Martensite Plates Form During Cooling | ement of the β phase, while the temperature Af is the temperature at which the last martensite plates disappear during the heating of the alloy.

A general overview of these and similar alloys is given in "Journal of Materials Science", 9 (1974). " 1521 to 1555, as well as in the manual "Shape Memory Effect in Alloys J. Perkins (Ed), Plenum Pi'ess, New York, 1975 · This manual also mentions virtual uses of these phenomena, for example, in building an engine or pump.

The present invention relates, in particular, to ternary copper-zinc-aluminum alloys of the β phase and it relates to the manufacture of solid bodies made up of these alloys and meeting the conditions required with regard to homogeneity and structure seeds. In this regard, it should be noted that the alloys do not necessarily have to be in the ß phase at room temperature, but that this phase can also appear at higher temperatures.

So far, copper-zinc-aluminum alloys of the crystal modification ß have been used in the form of polycrystalline solids obtained by casting. However, due to a too slow solidification rate or very rapid op *, the composition of a cast body is not sufficiently homogeneous and, in practice, the grains of this body are quite large. In the ß alloys referred to in this specification, the grains of a cast body have diameters of several millimeters, which is the cause of a fairly low mechanical resistance, not to mention that there can be ruptures. between the grains during mechanical processing.

The subject of the present invention is the manufacture of solid bodies of copper-zinc-aluminum alloys in the form of

The present invention provides a process for the production of solid bodies of copper-zinc-aluminum alloys under the crystal modification ß, this process being characterized in that it starts from a pulverulent material which, apart from the inevitable impurities, comprises 10 to 4-0% by weight of Zn, 1 to 12 $ by weight of Al, the rest being Cu, to then carry out a first cold compression of this pulverulent material which is then hot extruded under the shape of a solid body.

By doing so, the object of the invention can be achieved in an excellent manner. Thanks to the chosen starting composition of the powder, the body obtained has a ß or martensitic structure after cooling to its temperature of use. The compression and extrusion stages make it possible to obtain a solid body of a homogeneous composition and having a fine-grained structure. In practice, one can obtain a structure whose grains have an average diameter of 20 to 30 J ^ m · _ This structure with fine grains is attributable to the presence of a small proportion of A ^ O ^ in the powder of departure and, moreover, to a rapid cooling step after extrusion, but it should be noted that the invention is in no way limited to this theoretical explanation.

Due to its very homogeneous composition, the body obtained has practically equal properties over its entire length and its entire cross section. Due to the fine-grained structure, this body undergoes no rupture during mechanical processing. In addition, the body obtained has greater tensile strength and better resistance to fatigue than a body obtained by a casting process.

After the cold compression step, it is possible to adopt a hot compression step in order to confer higher densities on the material before the extrusion, but this step is not absolutely essential. On the other hand, the '' - s - '; | if one wants to obtain, from the initial powder, a solid body with good properties. If one adopts a simpler process, for example, compression of the powder followed by sintering, one does not can get a consistent solid body.

The solid body resulting from extrusion is, to a large extent, a semi-finished product in the form of a wire, a tube, a sheet or the like. Subsequently, these bodies can easily be transformed into final products having the desired shape and dimensions by means of a plastic molding, for example, hot or cold rolling. In most cases, the granularity hardly increases at this time.

When carrying out the process of the present invention, the starting material is a pulverulent material which, apart from the inevitable impurities, comprises 10 to 40 $ by weight of Zn, 1 to 12 $ by weight of Al, the rest being Cu. This composition is oriented towards a copper-zinc-aluminum alloy having a ß crystal structure. Several smaller intervals can be distinguished in the intervals contemplated here for composition and, therefore, apart from unavoidable impurities, a preferred powdery starting material comprises: (a) 24 to 32 $ by weight of Zn, 1 to 6 $ in weight of Al, the remainder being Cu, or (b) $ 18 to 24 by weight of Zn, 4 to $ 8 by weight of Al, the remainder being Cu, or (c) $ 10 to 18 in weight of Zn, 7 to 12 $ by weight of Al, the rest being Cu.

The expression “impurities”, used in this specification, designates elements naturally present in minute quantities in copper-zinc-aluminum alloys or elements occasionally incorporated into the powdery starting material during its preparation. These elements can be, for example, Si, Cr, Mn, Co, Fe and the like. Their proportion is generally only from 0 to 2 $ by weight, preferably from 0 to • V * · '♦ «'., '- - ..' · '*" ·' * · '* “· £ ν * · * / * 3

A small amount of oxygen fixed to form '*] oxides may be present in the pulverulent matter in addition to the impurities and the aforementioned elements. This oxygen can exert a certain effect on the grain structure of the solid body to be manufactured. quer and also on the transition temperatures. ; • 'It is believed that oxygen exists mainly in the form of Al ^ O ^ which exerts an inhibitory effect on grain growth, thus helping to ensure the fine grain structure of the product. However, it is understood that the invention is in no way limited to this explanation and, as a general rule, the oxygen content of the powder appears to be only 0.02 to 0.2 $ by weight · 'In general , the powdered starting material can be prepared in any suitable manner as long as its composition meets the conditions set out above. It seems very appropriate to adopt a preparation method in which. the copper, zinc and aluminum elements are melted together in a desired ratio, to then atomize the molten alloy obtained by means of a jet of water or another jet of fluid. However, it is also possible to carry out a simple mixing of the copper powder, of the zinc powder and of the aluminum powder in a desired ratio and it is also possible to add one or more of these elementary powders to a powdery alloy or to a powder mixture which has not yet reached its correct composition.

The powder compression step can be carried out by introducing it into a shell provided with a bottom, then by compressing the powder by means of a matrix. The pressure of this compression step can have any suitable value that the shell material and the powder can withstand: in practice, pressures of between 430 and 1,000 MKf / m2 have been adopted satisfactorily. In most cases cold compression may be sufficient, but this step may possibly be followed by hot compression, for example, - · '’**' 1 / ·. ' than cutting or turning, or even by a chemical process such as pickling. If possible, the compressed material can also be expelled from the shell.

After compression, the material obtained is first heated to a temperature suitable for extrusion, then extruded. Heating can be carried out in an oven in which a neutral or reducing atmosphere prevails. The appropriate temperature depends on the composition of the alloy, the capacity of the extrusion device, as well as the shape of the extruded body, this temperature can be, for example, between 700 and 800 ° C. j

In most cases, the press used for extrusion comprises a hollow die discharging the product in the form of a pro; semi-finished product such as a wire, a tube or a sheet, while this hollow die can possibly also be adapted for direct distribution of a final product. The extrusion speed must be sufficient to give a coherent solid body. On leaving the press, the extruded body is cooled to room temperature, this cooling can be carried out, for example, by sudden cooling with a cold liquid such as l 'eauo

If the extruded body is a semi-finished product, it can be further processed into a final product having the desired shape and dimensions by means of a rolling step or another mechanical deformation step.

Both the final product and the semi-finished product have an elastic recovery effect, a reversible elastic recovery effect and pseudo-elastic properties.

The invention will be illustrated by the following nonlimiting examples.

Examples X and IX

As starting material, a pulverulent alloy of Cu-Zn-Al is used whose chemical composition, structure gx-anu- * V t »ί · _, * '' * · '·, · I ·« · -' *, -. '* "·’'. Vjï • ^ of the type shown in Figure 1. The bottom 1 and the wall 2 of this. % shell are made of weak steel in the form of a one-piece body. The shell has an inside diameter of 82 mm, an outside diameter of 85 mm and a length of 110 mm. In this shell, comes a matrix 3 made of weak steel comprising an air hole 5 which can be closed by a plug 4 · This matrix 3 is conical on one side with an angle of attack of I4O0 in order to favor l subsequent extrusion of the shell contents. During the introduction of the powder, the shell is supported by a vibrating screen in order to obtain a good charge density. After having located the matrix 3j, the shell is introduced into a press, then the matrix 3 is lowered to carry out a cold compression step.

"

After the cold compression, the shell 2 is passed in turn to reach an outside diameter of 84 mm and the matrix 3 is welded to the wall of the shell in order to prevent oxidation of the powder. The shell and its contents are heated in an oven at 500 ° C for one hour. Then the shell is replaced in the press and its contents are subjected to hot compression.

After cooling, the shell is completely removed on a lathe. The compressed material is again deposited in the form of a billet in an oven and heated to 800 ° C for one hour. Then, the billet is placed in an extrusion press where it is extruded into a bar with a diameter of 10 mm using a conical hollow die having an angle of attack of 140 ° C.

Additional details regarding the cold compression, hot compression and extrusion steps are shown in Table B.

After extrusion, the bar obtained is immediately subjected to sudden cooling with water.

During radiographic and microscopic light examination, the material of the bars obtained in examples I and ί - m '- 9 - phases a and only a few colonies of martensite being present at the outer edge of the bar. During an electron microscope examination, it is found that Al ^ O ^ is dispersed in a gangue of Cu-Zn-Al and it is believed that this is the cause of an inhibition of the growth of grains.

The material of the bars has only a small granularity (see table B), while the grains are slightly elongated in the direction of extrusion. During the calcination, the growth of the grains does not increase more than 10 to 15% depending on the temperature and the duration of the calcination step.

The bars can be easily transformed into a final product in the form of a sheet with a thickness of 0.5 mm by means of hot rolling (oven temperature: 850 ° C). During this stage, the granularity increases to 130 µm perpendicular to the direction of rolling and to 175 µm in the direction of rolling, which is significantly lower than that obtained with a casting bar (200 ^ a minimum).

After carrying out a homogenization treatment (with sudden cooling), the bar is subjected to mechanical tests. The values obtained are shown in Table B.

After hot rolling, the values are somewhat lower,

The bars have an elastic recovery effect with a reversible elongation of $ 1.5 at temperatures above -60 ° C. The bars seem to have pseudo-elastic properties during the bending and stretching tests carried out at temperatures between 0 and 50 ° C. After application and removal of the load in order to achieve a pseudo-elastic elongation of $ 1.5, the residual plastic deformation is less than $ 0.05. In a tensile test, the pseudo-elastic hysteresis curve s '' # .., · r ''. - · ’’ VU: i · During bending tests carried out with applications i * ..; With repeated cations of the load, the fatigue strength is greater; many times greater than that obtained in cast bars ”;

V

I This resistance has a value between 100,000 and more than! 200,000 cycles for a pseudo-elastic elongation from 0.8 to 1%! under a maximum load of 250 MN / m2 against a value of 100 to; 20,000 cycles for cast alloys.

Example III

As a starting material, a powdery Cu-Zn-Al alloy obtained by melting the elements together and atomizing the molten material using water is used. Table A below gives the chemical composition, the granularity, the density and the crystal structure of this. alloy.

This powder is compressed in a shell of the type shown in FIG. 2, this shell consisting of a tube 6 of weak steel, a separate bottom 7 of hardened steel and a matrix 8 also of hardened steel. The tube has an inside diameter of 69 mm, an outside diameter of 70.4 mm and a length of 210 mm. This tube has, at. inside, a layer of zinc stearate acting as a lubricant. Next, the bottom 7 is placed and the powder is loaded into the shell which is supported by a vibrating sieve. After installing the die 8, the shell is placed in an extrusion press and its contents are subjected to cold compression by lowering the die.

After compression, the shell is removed from the press, its bottom 7 is removed and the tube 6 is cut to release the compressed material in the form of a billet. This billet has a density in the rough state of approximately 5.09 gfcm2, or $ 68 of the theoretical density. This billet is placed in an oven and heated to 800 ° C under an argon atmosphere for 3 hours. Then it is placed again in the extrusion press and extruded in the form of a bar 12.5 mm in diameter by means of a die. mi ancrlo rl'af + .amip rln 1 Rfl®. A == a "" Pîliôno '. -11-

Table B below provides additional details regarding the compression and extrusion steps.

The bar obtained has a density of 100¾. During radiographic and microscopic light examination, the material obtained appears to be mainly in the ß phase, a small amount of phase and only some colonies of martensite being present at the outer edge of the bar. Under the electron microscope, dispersed particles of Al ^ O ^ · can be distinguished. The material obtained has a granularity of 20 to 30 µm, while the grains are slightly elongated in the direction of extrusion. During calcination, the granularity increases only by 10 to 15% depending on the temperature and the duration of this calcination step.

By means of hot rolling (oven temperature: 850 ° C), the bar can be immediately transformed into a sheet with a thickness of 0.5 mm (final product). In this way, the granularity increases to 130 µm perpendicular to the direction of rolling and to 175 µm in the direction of rolling. These values are much lower than those obtained with cast bars (minimum 200 yrm).

The bar is subjected to mechanical tests without the need for a prior homogenization treatment (the material is sufficiently homogeneous). Table B below gives the values relating to the tensile strength, the elastic limit and the elongation. After hot rolling, these values are somewhat lower.

During bending and stretching tests carried out at a temperature between 0 and 50 ° C, the bar has pseudo-elastic properties and an elastic recovery effect.

After application and removal of a pseudo-elastic load in order to achieve an elongation of the residual plastic elongation seems to be less than 0.05¾. During a tensile test - 12 - larger than that of a casting bar.

During bending tests carried out with repeated applications of a load, the resistance to fatigue is much higher than that obtained with cast bars. This resistance is between 100,000 and more than 200,000 cycles at a pseudo-elastic elongation of 0.8 to 1% under a maximum tension of 25Ο MN / m2 against 100 to 20,000 cycles for cast alloys.

TABLE A Lighters used

Example I II III

Source "La Floridienne" "La Floridienne" Baudier further treatment ground in a mixed with device.d1a- of Cu brasion powder

Chemical composition : ·

Cu 72.22 73.05 76.04

Al ~ ζ} 30 6.11 8.22

Zn 20.09 19.49 15.68

Impurities 1.39 1.35 0.015

Oxygen content (% by weight) 0.146 0.050 0.0662

Granularity:

Interval 0.500 dxsa. '0,500 yjm 0,140 jxs d ^ 0 ISO jxsa. 178 yim 48 jrn

Bulk density 2 3.05 g / cm3 3.07 g / cm3 2.07 g / cm.

Flow density 1 4.26 g / cm3 3.57 g / cm3 3.11 g / cm.

Structure ß + marten- (3 + märten- β site site

According to ASTM B 527-70 standard.

2 Hall flowmeter according to ASTM standard.

1 * 3 i - 13 - Γ • * «j 1 TABLE B - |

Processing steps

Example I XI XIX

Cold compression Figure 1 Figure 1 Figure 1

Shell temperature Ambient Ambient Ambient

Pressure 1,000 MN / m2 1,000 MN / m2 430 MN / m2

Hot compression Figure 1 Figure 1 -

Temperature

shell 500 ° C 500 ° C

Pressure 1,000 MN / m2 1,000 MN / m2

Extrusion:

Temperature 800 ° C 800 ° C 800 ° C

Angle of attack 140 ° 140 ° l80 °

Extrusion ratio 71 * 5 71jS 32.2 - Product Barre Barre Barre!

Diameter 10 mm 10 mm 12.5 nun

Density 7.68 g / cm3 7.68 g / cm3 7d52 g / cm3, ($ 100 S) ($ 100) (100%)

Granularity 20-30 ^ a 20-30 ^ "1 20-30 jm.

Resistance to η ο o tensile y, 6xl0 N / m2 8.0x10 ° N / m2 8x10 ° N / m2 8 8 o

Elastic limit 4.7x10 N / m2 3.7x10 N / m2 1.9x10 ° LT / m2

Elongation at break 4% 1.5%> 6-8 $

Structure ß ß + märten- ß site

Claims (12)

1. A method of manufacturing solid bodies of copper-zinc-aluminum alloys having a crystal structure ß, characterized in that one starts from a pulverulent material which, apart from the inevitable impurities, comprises 10 to 40 $ by weight of Zn, 1 to 12 $. by weight of Al, the remainder being Cu, after which this pulverulent material is subjected to a first cold compression, then it is extruded hot to form a solid body. 2. Method according to claim 1, characterized in that one starts from a pulverulent material which, apart from the inevitable impurities, comprises 24 to 32 $ by weight of Zn, 1 to 6 $ by weight of Al, the rest being Cu. 3. Method according to claim 1, characterized in that one starts from a pulverulent material which, apart from the inevitable impurities, comprises 18 to 24 $ by weight of Zn, 4 to 8 $ by weight of Al, the rest being Cu. _ 4. Method according to claim 1, characterized in that one starts from a pulverulent material which, apart from the inevitable impurities, comprises 10 to 18 $ by weight of Zn, 7 to 12 $ by weight of Al, the rest being Cu. 5. Method according to any one of claims 1 to 4j characterized in that the powdery starting material is obtained by melting the elements Ζη, ΑΙ and Cu together in a desired ratio, to then subject the molten alloy obtained to atomization by means of a jet of fluid. 6. Method according to claim 1, characterized in that the cold compression step is followed by a hot compression step before the extrusion. 7. Method according to claim 6, characterized in that the hot compression step is carried out at a temperature of 500 to 600 ° C. - 15 - 8. Method according to claim 1, characterized in that the extrusion is carried out at a temperature of 700 to 800 ° C. 9 · A method according to claim 1, characterized in that the extruded body is cooled to room temperature by sudden cooling with a cold liquid * 10. Method according to claim 1, characterized in that, when it is a semi-finished product, the extruded body is transformed into a final product having the desired shape and dimensions moyennant by means of a rolling step or another step of mechanical deformation * 11 * Solid body consisting of a copper-zinc-aluminum alloy having a ß crystal structure and obtained by the process according to any one of claims 1 to 10, 12, solid body according to claim 11, characterized in that it has a granular structure with a granularity of between 20 and 30 µm "__%